Regular expressions question

Devils Child · 08-21-2009, 07:28 AM

hi!
Is it somehow possible to get use the regex "test*blah" and filter what's * out from the text?

Code:

			Regex regex = new Regex("test*blah");
			Match match = regex.Match("YYYtestXXXblahZZZ");
			if (match.Value == "XXX") MessageBox.Show("That's what I want!!!");

i suppose it must look like this, but i don't quite get what i want...

thanks in advance

tabstop · 08-21-2009, 07:55 AM

"Normally" you would use a regex like "test(.*)blah" and then use the backreference \1 to refer to the first parenthesized sub-expression (which in this case would appear to be what you want). The C# syntax for backreferences looks a little weird; if I'm reading it right, it would be something like

Code:

"test(?<1>.*)blah"

and then

Code:

"${1}"

in your Result would be what you want. (Of course, with this syntax you can give the thing a meaningful name, instead of "1".)

Cat · 08-21-2009, 08:35 AM

Here's the exact code you should need, including a named parameter:

Code:

// ExplicitCapture isn't strictly necessary, it makes sure no unnamed groups are captured.  
// If you only use named groups, turning ExplicitCapture on will improve speed and reduce memory usage.
Regex ex = new Regex(@"test(?'YourNamedParameter'.*)blah", RegexOptions.ExplicitCapture);

// This also works:
// Regex ex = new Regex(@"test(?<YourNamedParameter>.*)blah", RegexOptions.ExplicitCapture);

string input = "YYYtestXXXblahZZZ"

Match m = ex.Match(input);
if (m != null)
{
    string value = m.Groups["YourNamedParameter"].Value;
}

Here's a tutorial on how to make and use regular expressions, this is practically a regex bible:
Regular Expression Tutorial - Learn How to Use Regular Expressions

Devils Child · 08-21-2009, 09:13 AM

works like a charm. thanks for the quick reply

Devils Child · 08-21-2009, 09:35 AM

wait a minute: what's with this:
"testXXXblahYYYblah"

i should get: "XXX"
but i get "XXXblahYYY"

???

tabstop · 08-21-2009, 09:44 AM

Quote:

Originally Posted by Devils Child

wait a minute: what's with this:
"testXXXblahYYYblah"

i should get: "XXX"
but i get "XXXblahYYY"

???

Because that's what matches. Regex is greedy, and will always take the largest substring that fits the pattern.

Cat · 08-21-2009, 10:07 AM

Quote:

Originally Posted by tabstop

Because that's what matches. Regex is greedy, and will always take the largest substring that fits the pattern.

That's also covered in that regex tutorial I linked (in the chapter on repetition), but the non-greedy way would be to do this:

@"test(?'YourNamedParameter'.*?)blah"

Devils Child · 08-21-2009, 01:18 PM

works! thanks a lot

08-21-2009, 07:28 AM	#1
Devils Child Registered User Join Date: Jan 2008 Posts: 153	Regular expressions question hi! Is it somehow possible to get use the regex "testblah" and filter what's out from the text? Code: Regex regex = new Regex("test*blah"); Match match = regex.Match("YYYtestXXXblahZZZ"); if (match.Value == "XXX") MessageBox.Show("That's what I want!!!"); i suppose it must look like this, but i don't quite get what i want... thanks in advance
Devils Child is offline

08-21-2009, 07:55 AM	#2
tabstop and the Hat of Guessing Join Date: Nov 2007 Posts: 8,740	"Normally" you would use a regex like "test(.)blah" and then use the backreference \1 to refer to the first parenthesized sub-expression (which in this case would appear to be what you want). The C# syntax for backreferences looks a little weird; if I'm reading it right, it would be something like Code: "test(?<1>.)blah" and then Code: "${1}" in your Result would be what you want. (Of course, with this syntax you can give the thing a meaningful name, instead of "1".)
tabstop is offline

08-21-2009, 08:35 AM	#3
Cat Registered User Join Date: May 2003 Posts: 1,185	Here's the exact code you should need, including a named parameter: Code: // ExplicitCapture isn't strictly necessary, it makes sure no unnamed groups are captured. // If you only use named groups, turning ExplicitCapture on will improve speed and reduce memory usage. Regex ex = new Regex(@"test(?'YourNamedParameter'.)blah", RegexOptions.ExplicitCapture); // This also works: // Regex ex = new Regex(@"test(?<YourNamedParameter>.)blah", RegexOptions.ExplicitCapture); string input = "YYYtestXXXblahZZZ" Match m = ex.Match(input); if (m != null) { string value = m.Groups["YourNamedParameter"].Value; } Here's a tutorial on how to make and use regular expressions, this is practically a regex bible: Regular Expression Tutorial - Learn How to Use Regular Expressions __________________ You ever try a pink golf ball, Wally? Why, the wind shear on a pink ball alone can take the head clean off a 90 pound midget at 300 yards. Last edited by Cat; 08-21-2009 at 08:39 AM.
Cat is offline

08-21-2009, 09:13 AM	#4
Devils Child Registered User Join Date: Jan 2008 Posts: 153	works like a charm. thanks for the quick reply
Devils Child is offline

08-21-2009, 09:35 AM	#5
Devils Child Registered User Join Date: Jan 2008 Posts: 153	wait a minute: what's with this: "testXXXblahYYYblah" i should get: "XXX" but i get "XXXblahYYY" ???
Devils Child is offline

08-21-2009, 01:18 PM	#8
Devils Child Registered User Join Date: Jan 2008 Posts: 153	works! thanks a lot
Devils Child is offline

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